Timeline for How does a Frost diagram reproduce the solutions to the wave equation?
Current License: CC BY-SA 3.0
13 events
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| Jan 7, 2018 at 14:27 | history | edited | orthocresol | CC BY-SA 3.0 |
touchup
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| Aug 15, 2016 at 17:51 | history | edited | ron | CC BY-SA 3.0 |
reformatted "+' symbol from exponent to in-line
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| Oct 28, 2014 at 5:52 | vote | accept | Dissenter | ||
| Sep 27, 2014 at 1:56 | comment | added | Philipp |
@EricBrown There is no physical reason that one "puts the polygon on its point" and draws energy levels at the intersections. In which sense do you mean that? The equation for the Hückel energy levels, $e_{j} = \alpha + 2 \beta \cos \frac{2 j \pi}{N}$, gives you that equilateral polygon shape and since the level for $j=0$ is always non-degenerate and the lowest-lying level ($\beta$ is negative) its tip will always be at the bottom. Or do I misunderstand you?
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| Sep 27, 2014 at 1:52 | history | edited | ron | CC BY-SA 3.0 |
added 487 characters in body
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| Sep 26, 2014 at 23:41 | comment | added | Eric Brown | Frost-Muselin method is simply a mnemonic to the solution for the secular equations of this very small set of per-cis annulenes. There is no physical reason that one "puts the polygon on its point" and draws energy levels at the intersections. And to add to the discussion about how Hueckel theory is generally wrong for ground state of highest symmetry planar "anti-aromatic" species: they are ground state singlet even before J-T distortion (violations of Hund's rule in molecules) | |
| Sep 26, 2014 at 16:50 | comment | added | ron | @GeoffHutchison Thanks Geoff, you said it much better than I did with my cyclooctatetraene-cyclobutadiene analogy. | |
| Sep 26, 2014 at 16:00 | comment | added | Geoff Hutchison | @ron I'd point out that cyclobutadiene basically undergoes a Jahn-Teller like distortion, which eliminates the triplet character and lowers the total energy. It's not that Frost is wrong, just that cyclobutadiene doesn't exist with equal length bonds. | |
| Sep 26, 2014 at 15:18 | comment | added | ron | Huckel's rule only applies to a small, highly-defined class of molecules. For example, it predicts that cyclooctatetraene is antiaromatic; in fact, the molecule distorts from planarity and is stable. Frost predicts 2 degenerate non-bonding MOs at 0 beta for cyclobutadiene; in fact, the molecule distorts and the MO's split. | |
| Sep 26, 2014 at 15:11 | comment | added | Dissenter | @ron what are the weak points of Huckel's rule? | |
| Sep 26, 2014 at 14:45 | comment | added | ron | It works because it is an extension of Huckel's 4n+2 rule. Since it is related to Huckel's rule, it has its weak points, just like Huckel's rule. | |
| Sep 26, 2014 at 14:31 | comment | added | Dissenter | But why does this work? | |
| Sep 26, 2014 at 14:29 | history | answered | ron | CC BY-SA 3.0 |